Storage apparatus and control method therefor

ABSTRACT

A storage apparatus comprises at least one housing A in which a storage device and a controller are provided, at least one housing B in which a storage device and a peripheral device are provided, and a transmission path for connecting the storage device and the controller of the housing A, and the storage device of the housing B to enable communication therebetween. The storage apparatus is capable of controlling operation of the storage device of the housing B according to an operating state of the storage device of the housing A through communication via the transmission path; and controlling operation of the peripheral device according to an operating state of the storage device of the housing B.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority upon Japanese Patent ApplicationNo. 2002-174948 filed June 14, 2002, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage apparatus and a controlmethod therefor.

2. Description of the Related Art

There are known disk array devices that have a configuration in whichhousings, each of which accommodating a plurality of disk drives, aremounted in several layers. Such disk array devices are called“rackmount” disk array devices. Japanese Patent Application Laid-openPublication No. 2001-339853 discloses a power supply method for such atype of disk array device. According to the method disclosed, apower-supply apparatus is provided outside the housing and connected toa basic housing and an extension housing by dedicated control lines forcontrolling power supplied to the housings in such a way that the powersupplied to the extension housing is turned ON/OFF in an interlockedmanner with the ON/OFF of the power supplied to the basic housing.

In such a disk array device, the power-supply apparatus must be providedoutside the housing and, in addition, it is necessary to providededicated control lines therefor. For this reason, problems inminiaturization and cost arise. In order to solve these problems,another type of a disk array device is known in which only a minimumnumber of cables are provided as wires for mutually connecting thehousings and those cables are used for transmitting read data and writedata as well as for exchanging a variety of control signals. Inaddition, some of the disk array devices, which have a minimum number ofcables as described above, are capable of keeping some of the componentsin the extension housings ON even while the power of the disk drives inthe basic housing is OFF. Then, when the operation of the disk drives inthe basic housing is started, the extension housings recognize that thedisk drives in the basic housing have started to operate, and start tofully operate as well.

In a disk array device having such a configuration, while the powersupplied to the disk drives of the basic housing is in an OFF state, inthe extension housings, only the components required to recognize thestart of the operation in the basic housing are kept ON. That is, theoperation state of the extension housings is different from that of whenthe extension housings are ON. For example, the amount of heatdissipated by the various devices mounted on the extension housings whenonly the components for start recognition are operated is smaller thanthe amount of heat dissipated when the power of the extension housingsis ON. Therefore, from power-saving and noise-reduction points of view,it is preferable to make peripheral devices mounted on the basichousing, such as cooling fans, to operate in a state that is appropriateto cool the dissipated heat.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a storage apparatus anda storage apparatus control method enabling the storage apparatus to becontrolled in a state desirable for power saving and noise reduction.

To achieve the above and other objects, one aspect of the presentinvention provides a method of controlling a storage apparatus. Thestorage apparatus includes: at least one housing A in which a storagedevice and a controller are provided; at least one housing B in which astorage device and a peripheral device are provided; and a transmissionpath for connecting the storage device and the controller of the housingA, and the storage device of the housing B to enable communicationtherebetween. The method comprises: controlling operation of the storagedevice of the housing B according to an operating state of the storagedevice of the housing A through communication via the transmission path;and controlling operation of the peripheral device according to anoperating state of the storage device of the housing B.

Features and objects of the present invention other than the above willbecome clear by reading the description of the present specificationwith reference to the accompanying drawings.

According to the present invention, it becomes possible to, for example,control a storage apparatus in a preferable manner for saving power andreducing noise.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described byreferring to accompanying diagrams in which:

FIG. 1A is a front view of a disk array device 10 according to anembodiment of the present invention, and FIG. 1B is a rear view of thedisk array device 10;

FIG. 2A is a perspective view of a basic housing 20, which is mounted onthe disk array device 10 according to the embodiment of the presentinvention, as seen from the front thereof, and FIG. 2B is a perspectiveview of the basic housing 20 as seen from behind;

FIG. 3A is a perspective view of an extension housing 30, which is alsomounted on the disk array device 10 according to the embodiment of thepresent invention, as seen from the front thereof, and FIG. 3B is aperspective view of the extension housing 30 as seen from behind;

FIG. 4 is a diagram showing a configuration of a disk drive 51 mountedon a disk-drive unit 52 according to the embodiment of the presentinvention;

FIG. 5 is a diagram showing a circuit configuration of the disk arraydevice according to the embodiment of the present invention;

FIG. 6 is a flowchart showing a sequence of processes carried out by thedisk array device according to the embodiment of the present inventionwhen a main switch 75 is turned OFF;

FIG. 7 is a diagram showing operating states of disk drives 51α, 51β anda cooling fan 66, which are employed in the disk array device accordingto the embodiment of the present invention, when the main switch 75 isturned ON and OFF; and

FIG. 8 is a flowchart showing a sequence of processes carried out by thedisk array device according to the embodiment of the present inventionwhen the main switch 75 is turned ON.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention are described indetail by referring to the accompanying diagrams below.

===Outline of the Disclosure===

At least the following will be apparent in accordance with the presentspecification and accompanying drawings.

One aspect of the present invention is a method of controlling a storageapparatus. The storage apparatus includes: at least one housing A inwhich a storage device and a controller are provided; at least onehousing B in which a storage device and a peripheral device areprovided; and a transmission path for connecting the storage device andthe controller of the housing A, and the storage device of the housing Bto enable communication therebetween. The method comprises: controllingoperation of the storage device of the housing B according to anoperating state of the storage device of the housing A throughcommunication via the transmission path; and controlling operation ofthe peripheral device according to an operating state of the storagedevice of the housing B.

An example of the storage apparatus is a disk array device having aconfiguration in which one or more housings are provided in a rackframe. The storage device cited above is, for example, a disk drive. Thehousings A and B are, for example, the basic and the extension housingsrespectively. An example of the peripheral device is a cooling devicesuch as a cooling fan of the air cooling type for exhausting heatdissipated in the housing to the outside of the housing. An “operatingstate of a storage device” is, for example, ON and OFF states of a diskdrive as well as the ‘Ready’, ‘Not Ready’ and ‘Power Supply OFF’ statesto be described later. “Controlling operation of the peripheral deviceof the housing B” means, for example, to decrease the rotation speed ofthe cooling fan (which is an example of a peripheral device of theextension housing), or to decrease the number of cooling fans to beoperated, which will be described later. The “communication via thetransmission path” means, for example, communications through alater-described FC-AL loop 60 such as: communication between the diskdrives 51 and the controller 71 accommodated in the basic housing 20;communication between the controller 71 in the basic housing 20 and maindisk drives 51α or sub-disk drives 51β in the extension housing 30; andcommunication between the controller 71 in the basic housing 20 and asub-controller 81 in the extension housing 30.

In the configuration described above, it is possible to, for example,make peripheral devices, such as cooling fans, operate in an appropriatemanner for operating the storage device in the housing B when the powerof the storage device of the housing A is turned OFF. Therefore, itbecomes possible to control the storage apparatus in a preferable mannerfor saving power and reducing noise.

===Apparatus Configuration===

FIG. 1A is a front view of a disk array device 10 according to anembodiment of the present invention, and FIG. 1B is a rear view of thedisk array device 10. FIG. 2A is a perspective view of a basic housing20, which is mounted on the disk array device 10, as seen from the frontthereof, and FIG. 2B is a perspective view of the basic housing 20 asseen from behind. FIG. 3A is a perspective view of an extension housing30, which is also mounted on the disk array device 10, as seen from thefront thereof, and FIG. 3B is a perspective view of the extensionhousing 30 as seen from behind.

As shown in FIGS. 1A and 1B, the disk array device 10 has aconfiguration based on a rack frame 11. The rack frame 11 has aplurality of stages of mount frames 12 in the vertical direction and onboth the right and left side surfaces inside the rack frame 11. Themount frames 12 are oriented in the horizontal direction from the rearof the rack frame 11 to the front thereof. The basic housing 20 or theextension housing 30 is placed on the mount frames 12 like a drawer. Asshown in FIGS. 2A, 2B, 3A, and 3B, the basic housing 20 or the extensionhousing 30 have various boards and units for implementing a variety offunctions of the disk array device 10.

As shown in FIG. 2A, on the upper section of the front of the basichousing 20, a plurality of disk-drive units 52 are lined up. Each of thedisk-drive units 52 includes a disk drive 51.

On the lower section of the front of the basic housing 20, there aremounted a battery unit 53, a display panel 54 for displaying, forexample, the operation state of the disk drives 51, and a flexible-diskdrive 55. The battery unit 53 has inside a secondary battery. Thebattery unit 53 serves as a backup power supply, which is used forsupplying power to the boards and the units when the supply of powerfrom an AC/DC power supply 57 is cut off due to power failure or thelike. The display panel 54 has display devices such as LED lamps thatare used for displaying the operation state of the disk drives 51 or thelike. The flexible-disk drive 55 is used, for example, to load amaintenance program.

As shown in FIG. 2B, on the upper level of the rear on each side of thebasic housing 20, a sub-controller board 56 is provided. Thesub-controller board 56 has: a PBC (Port Bypass Circuit) 50 (not shownin this figure) for controlling an FC-AL loop (Fibre Channel ArbitratedLoop) 60 formed between the disk drives 51; and circuits for monitoringthe state of the AC/DC power supply 57, monitoring the states of thedisk drives 51, controlling the display devices on the display panel 54,monitoring the temperature of each component in the housing, and forvarious other purposes. The sub-controller board 56 also includes aFibre Channel-cable connector 67. To the connector 67 is connected aFibre Channel cable 91, which is part of the route of the FC-AL loop 60.It is to be noted that details of the FC-AL loop 60 are described indocuments such as “Description of Fibre Channel Technology” (FibreChannel Industry Association Japan, published: Ronsosha), JapanesePatent Application Laid-open Publication No. 2001-167040, JapanesePatent Application Laid-open Publication No. 2001-337868, and JapanesePatent Application Laid-open Publication No. 2001-222385.

As shown in FIG. 2B, in a space between the two sub-controller boards 56provided on the upper level of the rear on both sides of the basichousing 20, two AC/DC power supplies 57 are mounted next to each other.The AC/DC power supplies 57 supply power to the boards and the units. Itis to be noted that each of the basic housing 20 and the extensionhousing 30 is provided with two AC/DC power supplies 57 in order toassure security of power supply for the basic housing 20 and theextension housing 30. The AC/DC power supply 57 has a breaker switch 64for turning the output of the AC/DC power supply 57 ON and OFF.

As shown in FIG. 2B, beneath the AC/DC power supplies 57, two coolingfan units 58 of the air cooling type are arranged next to each other.The cooling fan unit 58 has at least one cooling fan 66. By blowing airinto and out of the housing, the cooling fan 66 exhausts heat dissipatedby components, such as the disk drives 51 and the AC/DC power supply 57,to the outside of the housing. It is to be noted that air paths and airholes are formed on each of the basic housing 20, the extension housing30, the boards, and the units for allowing air to be circulated insidethe basic housing 20 and the extension housing 30, thus enabling thecooling fans 66 to efficiently exhaust heat from the insides of thebasic housing 20 and the extension housing 30 to the outside. Thecooling fan unit 58 is connected to a controller board 59 or asub-controller board 56 by a control line 48 so that the controllerboard 59 or the sub-controller board 56 is capable of controlling therotation speed (number of rotations) of the cooling fan 66 employed inthe cooling fan unit 58 through the control line 48.

As shown in FIG. 2B, on the lower level of the rear of the basic housing20, two controller boards 59 are mounted in the vertical direction. Thecontroller board 59 has, for example: a communication interface betweenthe disk drives 51α and 51β mounted on the basic housing 20 and theextension housing 30, respectively; circuit(s) for controlling theoperations of the disk drives 51 (for example, according to RAIDcontrol) and for monitoring the states of the disk drives 51; acommunication interface board 61 for providing a communication functionconforming to, for example, SCSI or Fibre Channel specifications inorder to provide functions as a communication interface with the hostcomputer 40; and a cache memory 62 for storing data to be written into adisk drive 51 and data read out from a disk drive 51. The communicationinterface board 61 mounted on the controller board 59 has an externalconnector 63 conforming to predetermined interface specifications suchas the SCSI specifications or specifications of a LAN for connecting tothe host computer 40 and built in compliance with a protocol such as theFibre Channel or Ethernet protocol. The disk array device 10 isconnected to the host computer 40 by a communication cable 92 connectedto this external connector 63.

As shown in FIG. 3A, on the front-surface side of the extension housing30, a plurality of disk-drive units 52 are arranged next to each other.Each of the disk-drive units 52 includes a disk drive 51. As shown inFIG. 3B, on each side of the rear of the extension housing 30, asub-controller board 56 is provided. In addition, in a space between thetwo sub-controller boards 56 provided on the rear on each side of theextension housing 30, two AC/DC power supplies 57 are arranged next toeach other. Furthermore, beneath the AC/DC power supplies 57, twocooling fan units 58 are arranged next to each other.

FIG. 4 is a diagram showing a typical configuration of a disk drive 51mounted in a disk-drive unit 52. The disk drive 51 is an ordinary diskdrive of the 3.5-inch type employed in a commonly known general personalcomputer. The disk drive 51 has, for example: mechanical parts, such asan actuator 101, a spindle motor 72, a disk 73, and a head 74 forreading and writing data; a mechanism control circuit 105 forcontrolling the mechanical parts; a signal-processing circuit 106 forcontrolling a read/write signal supplied to the disk 73; acommunication-interface circuit 107; an interface connector 79 throughwhich various commands and data to be written/read to/from the disk 73are input/output; and a power-supply connector 80.

<Circuit Configuration>

With the basic housing 20 and the extension housing(s) 30 mounted in therack frame 11, the boards and the units mounted on the housings 20 and30 are connected to each other by, for example, internal wires, internalcircuits, and external wires to form a circuit shown in FIG. 5. Theinternal wires, the internal circuits, and the external wires aremounted on the rack frame 11 but not shown in the figures. In FIG. 5, athick line represents the FC-AL loop 60, a thin line represents acontrol line 48, and a dashed line represents a power-supply line 49.The controller 71 is a circuit comprising components such as a CPU, aprotocol control chip, and a memory such as a RAM and a ROM. Thecomponents of the controller 71 are mounted on the controller board 59.The controller 71 carries out functions such as a function tocommunicate with the host computer 40 and functions to control andmonitor the disk drives 51α and 51β respectively mounted on the basichousing 20 and the extension housing 30.

A main switch 75 is provided, for example, on the front surface of thebasic housing 20 in such a way that, for example, when the controllerboard 59 is mounted on the basic housing 20, an output signal line 77 ofthe main switch 75 is connected to the controller 71. It is to be notedthat the main switch 75 can also be provided on the rack frame 11. Inthis case, the system can be configured so that, when the basic housing20 is mounted on the rack frame 11, the output signal line 77 of themain switch 75 is connected to the controller 71.

One reason why the main switch 75 is provided as a switch separate fromthe breaker switch 64 of the AC/DC power supply 57 is to eliminate theneed to carry out burdensome manual operations. For example, if thebreaker switches 64 of all of the AC/DC power supplies 57 of the basichousing 20 and the extension housing 30 are turned OFF, not only theAC/DC power supply 57 of the basic housing 20 but also the AC/DC powersupplies 57 of the extension housings 20 have to be turned ON in orderto restart the disk array device 10. Further, before turning the breakerswitch 64 of the basic housing 20 ON, it would be necessary to firstturn the breaker switches 64 of the extension housings 30 ON in advanceand confirm that all of the disk drives 51 mounted on the extensionhousings 30 have started operating. By providing the main switch 75 as aswitch separate from the breaker switch 64, in case, for example, thedisk array device 10 is to be restarted in a relatively short period oftime, it becomes possible to restart the disk array device 10 by turningonly the main switch 75 OFF, without turning the breaker switches 64OFF, and then turning the main switch 75 ON according to a mechanismdescribed later.

Furthermore, the main switch 75 is also for providing an opportunity toperform so-called destaging, which is a process for storing, onto thedisk 73, data unwritten to the disk drive 51 and left in the cachememory 62, when turning the disk array device 10 completely OFF byturning OFF the breaker switch 64. For example, when the operator or thelike intends to stop the operation of the disk array device 10, theoperator first turns off the main switch 75 before turning off thebreaker switch 64. Detecting that the main switch 75 has been turnedOFF, the controller 71 destages data left in the cache memory 62 andunwritten to the disk 73. Then, after destaging of the unwritten data iscompleted, the controller 71 displays a message indicating thecompletion of the de-stage operation on the display panel 54. Informedby the message that destaging has been completed, the operator turns offthe breaker switch 64 to stop the operation of the disk array device 10.It is to be noted that, in order to restart the disk array device 10,the operator needs to turn on the breaker switch 64 first before turningon the main switch 75.

In addition, the controller 71 is also capable of performing controlcorresponding to the ON/OFF operations of the main switch 75 usingsoftware. For example, the controller 71 is capable of performingcontrol corresponding to the ON/OFF operations of the main switch 75 inremote control based, for example, on a signal input from the externalconnector 63. In the case of a configuration in which only the breakerswitch 64 is used without employing the main switch 75, when the breakerswitch 64 is turned off, all power supplied to the disk array device 10is cut off inevitably, making it impossible to receive an ON/OFF signalfrom an external source and, hence, impossible to execute the remotecontrol. It is therefore necessary to provide the main switch 75 inorder to enable ON/OFF operation control using software.

The PBC 50 mainly provides a function to interconnect the disk drives 51and the controller 71, which are accommodated in the basic housing 20and/or the extension housings 30, by using the FC-AL loop 60. It is tobe noted that the circuit board of the PBC 50 is provided in the rackframe 11 of the disk array device 10 or, as an alternative, some or allof the circuit board may be mounted on the controller board 59 and/orthe sub-controller board 56.

As described above, the PBC 50 mainly functions to connect the diskdrives 51 and the controller 71 to each other via the FC-AL loop 60. Inaddition, the PBC 50 also plays the role of disconnecting a failed diskdrive 51 from the FC-AL loop 60 and, when a new disk drive 51 ismounted, incorporating that new disk drive 51 to the FC-AL loop 60.

A sub-controller 81 is mounted on the sub-controller board 56. Thesub-controller 81 is configured from, for example, a CPU, a memory suchas a RAM and a ROM, as well as a variety of other control chips. Thesub-controller 81 has control lines 48 that are connected to the coolingfan unit 58 and the AC/DC power supply 57. The sub-controller 81controls and monitors the boards and the units, such as the cooling fanunits 58, the AC/DC power supplies 57, and the disk drives 51, mountedon the basic housing 20 and the extension housing 30.

===Description of Operations===

<Operating States of the Disk Drive>

Receiving a command from the controller 71, the disk drive 51 enters a‘Ready’, ‘Not Ready’ or ‘Power Supply OFF’ operating state. The diskdrive 51 operating in the ‘Ready’ state is capable of further receivinga data-read or data-write command issued by the controller 71. The disk73 mounted in the disk drive 51 operating in the ‘Ready’ state isrotating at a rotation speed required for an operation to read out orwrite data from or into the disk 73. The state of rotating at such arotation speed is referred to as a “spin-up state” of the disk 73. It isto be noted that an average power consumption of the disk drive 51 inthe ‘Ready’ state is the greatest among the three states mentionedabove.

When the disk drive 51 is operating in the ‘Not Ready’ state, the disk73 of that disk drive 51 is not rotating at the rotation speed requiredto read out or write data from or into the disk 73. That is to say, thedisk 73 is in a “spin-down state”. It is to be noted that the disk drive51 operating in the ‘Not Ready’ state cannot receive a command to readout or write data from or onto the disk 73; however, it can acceptcommands of a specific type such as a command for making the disk drive51 change to the ‘Ready’ state. Note that the average power consumptionof the disk drive 51 in the ‘Not Ready’, operating state is smaller thanthe average power consumption of the disk drive 51 in the ‘Ready’operating state.

When the disk drive 51 is operating in the ‘Power Supply OFF’ state, thedisk drive 51 is not capable of receiving a command issued by thecontroller 71. In addition, the rotation of the disk 73 mounted on thedisk drive 51 is completely stopped. It is to be noted that the averagepower consumption of the disk drive 51 in the ‘Power Supply OFF’operating state is zero.

The disk drive 51 is also provided with SES (SCSI Enclosure Service) andESI (Enclosure Service I/F) functions, which are prescribed in SCSI-3(Small Computer System Interface 3) specifications. By wiringpredetermined signal pins of the interface connector 79, the SES (SCSIService) and ESI (Enclosure Service I/F) functions can be operated. Itis to be noted that, in the following description, a disk drive 51carrying out these functions is referred to as a main disk drive 51αwhile a disk drive 51 not carrying out these functions is referred to asa sub-disk drive 51β.

<Basic Operations of the Disk array device>

The controller 71 can determine whether each of the disk drives 51 is inthe ‘Ready’, ‘Not Ready’ or ‘Power Supply OFF’ operating state bycommunicating with disk drives 51 mounted on the basic housing 20 andthe extension housing 30 through the FC-AL loop 60. In addition, thecontroller 71 transmits a command to a disk drive 51 to control theoperation of the disk drive 51. It is to be noted that communicationsfor detecting the operating states and for operation control are carriedout in accordance with a protocol such as FC-AL or the Fibre Channelprotocol for SCSI.

<Turning the Main Switch OFF>

With reference to a flowchart shown in FIG. 6, a sequence of processescarried out by the disk array device 10 having the configurationdescribed above when the main switch 75 is turned OFF will be describedbelow.

First of all, it is assumed that the breaker switches 64 of all theAC/DC power supplies 57 mounted on the basic housing 20 and theextension housing 30 are in an ON state while the main switch 75 is inan ON state, and thus all the power supplies of the disk drives 51mounted on the basic housing 20 and the extension housing 30 are ON.

In this state, the operator or the like turns off the main switch 75 atstep S611 of the flowchart shown in FIG. 6. When detecting thisoperation to turn off the main switch 75, the controller 71 halts theservice for the host computer 40 and starts a destaging process ofunwritten data left in the cache memory 62 at step S612. After thedestage process is completed, the controller 71 sends a command tosub-disk drives 51β mounted in the basic housing 20 and the extensionhousing 30 through the FC-AL loop 60 at step S613, requesting thesub-disk drives 51β to make a transition from the ‘Ready’ operatingstate to the ‘Power Supply OFF’ operating state. As a result, thesub-disk drives 51β mounted in the basic housing 20 and the extensionhousing 30 enter the ‘Power Supply OFF’ operating state at step S614.

The controller 71 is monitoring the operating state of each disk drive51 mounted in the basic housing 20 and the extension housing 30 bysending out an inquiry to each of the disk drives 51 through the FC-ALloop 60 (such as by polling). When the controller 71 detects that asub-disk drive 51β mounted in a certain extension housing 30 has made atransition to the ‘Power Supply OFF’ operating state, the controller 71sends, to the sub-controller 81 of the extension housing 30 via theFC-AL loop 60, a command to lower the rotation speed of the cooling fan66 employed in the cooling-fan unit 58 mounted in the relevant extensionhousing 30 at step S615. Receiving the command, the sub-controller 81reduces the rotation speed of the cooling fan 66 by, for example,lowering a driving voltage applied to the cooling fan 66 at step S616.

On the other hand, at step S617, the controller 71 sends a command tothe main disk drives 51α mounted in the extension housing 30 in the rackframe 11 through the FC-AL loop 60, requesting the main disk drives 51αto make a transition to the ‘Not Ready’ operating state. As a result,the main disk drives 51α mounted in the extension housing 30 enter the‘Not Ready’ operating state at step S618.

In this state, power is supplied to the sub-controller board 56 in eachextension housing 30, and therefore, the sub-controller 81 is capable ofcontinuing its function. In addition, as described above, in the ‘NotReady’ operating state, the main disk drive 51α do not accept data-readcommands or data-write commands; however, they accept some specificcommands such as a command for instructing transition from one of theabove-mentioned operating state to another operating state. In addition,by making the main disk drives 51α operate in the ‘Not Ready’ operatingstate, the power consumption of the main disk drives 51α becomes smallerin comparison with that in the ‘Ready’ operating state. Furthermore,since the operations of the sub-disk drives 51β are also halted, theoverall power consumption of the disk array device 10 becomes extremelysmall.

It is to be noted that in order to perform the control processesmentioned above, for example, the sub-disk drive 51β can send, to thecooling-fan unit 58α, a command instructing to lower the rotation speed,and an MPU mounted on the cooling-fan unit 58 can actually perform thecontrol. The rotation speed of the cooling fan 66 is reduced to a valueappropriate for the operating state of the disk drives 51. In thisembodiment, for example, 2 main disk drives 51α are operating in the‘Not Ready’, state while the sub-disk drives 51β are operating in a‘Power Supply OFF’ state. In this case, the rotation speed of thecooling fan 66 is reduced to a value appropriate for exhausting heatdissipated by the disk drives 51 operating in such states. It is to benoted that the main disk drives 51α and the sub-disk drive 51β may notchange to the ‘Not Ready’, and ‘Power Supply OFF’ state synchronously;instead, they may change to the ‘Power Supply OFF’ state with adifference in time. In view of such a situation, the system can beconfigured so that the controller 71 or the sub-controller 81 in theextension housing 30 or the like monitors the operating states of themain disk drives 51α and the sub-disk drive 51β on a real-time basis orat short time intervals so as to precisely control the rotation speed ofthe cooling fan 66 in accordance with the operating states of the maindisk drives 51α and the sub-disk drive 51β, which change from time totime. In addition, it is also possible to provide a configuration inwhich an optimum rotation speed is automatically set in accordance witha temperature detected by a sensor or the like.

Then, at step S619, the controller 71 controls the sub-controller 81 inthe basic housing 20 through the control line 48 to halt the rotation ofthe cooling fan 66 in the basic housing 20. Then, at step S620, thecontroller 71 causes the main disk drives 51α mounted in the mainhousing 20 to make a transition to the ‘Power Supply OFF’ operatingstate. In this way, the sequence of processes carried out when the mainswitch 75 is turned OFF is completed.

FIG. 7 is a diagram showing operating states of the disk drives 51α, 51βand the cooling fan 66, which are incorporated in the basic housing 20and the extension housing 30, according to the state of the main switch75.

When the main switch 75 is ON, all the disk drives 51α and 51βincorporated in the basic housing 20 and the extension housing 30 areoperating in the ‘Ready’ state. The cooling fan 66 is driven at a highrotation speed required for exhausting heat generated in the basichousing 20 and the extension housing 30 in this operating state.

When the main switch 75 is OFF, on the other hand, the power supplies ofall the disk drives 51α and 51β incorporated in the basic housing 20 areturned off. As for the extension housing 30, the power supply of thesub-disk drive 51β is turned off, and only the main disk drive 51α isoperating in the ‘Not Ready’ state. The cooling fan 66 is driven at arotation speed required for exhausting heat generated in this operatingstate. This rotation speed is lower than the rotation speed when themain switch 75 is ON. That is to say, when the main switch 75 is OFF,the cooling fan 66 of the extension housing 30 is driven at a rotationspeed lower than the rotation speed when the main switch 75 is ON;therefore, power saving and noise reduction can be accomplished.

It is to be noted that, in the above description, the rotation speed ofthe cooling fan 66 is controlled in accordance with the operating stateof the disk drives 51 in order to save energy and reduce noises.However, it is also possible to provide a configuration in which, forexample, the sub-controllers 81 control the AC/DC power supplies 57 inaccordance with the operating states of the disk drives 51 to adjust thenumber of operating cooling fans 66 in order to save energy and reducenoises as well.

<Turning the Main Switch ON>

With reference to a flowchart shown in FIG. 8, description will be madeof a sequence of processes carried out by the disk array device 10having the configuration described above when the main switch 75 isturned ON again after being once turned OFF with the breaker switch 64turned ON.

When the controller 71 detects that the main switch 75 has been turnedON at step S811 of the flowchart shown in FIG. 8, the controller 71controls the sub-controller 81 of the basic housing 20 through thecontrol line 48 to start an operation to supply power to the main diskdrives 51α in the basic housing 20 at step S812. At step S813, thecontroller 71 also controls the sub-controller 81 of the basic housing20 through the control line 48 to start making the cooling fan 66 of thebasic housing 20 to rotate at a required rotation speed. Further, atstep S814, the controller 71 sends a command to the main disk drives 51αin the basic housing 20 and the extension housing 30 through the FC-ALloop 60, requesting the main disk drives 51α to make a transition to the‘Ready’ operating state. As a result, the main disk drives 51α in thebasic housing 20 make the transition to the ‘Ready’ operating state.

Then, the controller 71 sends a command to the sub-controller 81 in theextension housing 30 through the FC-AL loop 60, requesting thesub-controller 81 to raise the rotation speed of the cooling fan 66.Receiving this command, the sub-controller 81 increases the rotationspeed of the cooling fan 66 at step S815. It is to be noted that, atthis stage, the rotation speed of the cooling fan 66 can be increased inadvance to a value required for exhausting heat that will be dissipatedwhen all the disk drives 51α and 51β incorporated in the extensionhousing 30 are put in the ‘Ready’, operating state. In this way, it ispossible to prevent the sub-disk drives 51β from making a transition tothe ‘Ready’, operating state faster than the rise of the rotation speedof the cooling fan 66 and, hence, to prevent the temperature in thehousing from increasing. Instead, the rotation speed of the cooling fan66 can be gradually increased in accordance with the state of transitionof each of the main disk drives 51α and/or the sub-disk drives 51β. Asan alternative, instead of varying the rotation speed of the cooling fan66, the number of operating cooling fans 66 can be adjusted. In thiscase, the number of operating cooling fans 66 can be gradually increasedin accordance with the state of transition of each of the main diskdrives 51α and/or the sub-disk drives 51β. As described above, by makingthe cooling fan 66 rotate in a state that is appropriate for theoperation state at different times, it becomes possible to save energyand reduce noises effectively.

Then, the controller 71 sends a command to the sub-controllers 81 in themain housing 20 and the extension housing 30 through the FC-AL loop 60and the control line 48, requesting the sub-controllers 81 to startsupplying power to the sub-disk drives 51β. Receiving this command, atstep S816, the sub-controllers 81 in the main housing 20 and theextension housing 30 control the AC/DC power supplies 57 to startsupplying power to the sub-disk drives 51β that they are in charge of.In this way, each of the sub-disk drives 51β starts operating in the‘Not Ready’ state.

By sending an inquiry through the FC-AL loop 60, for example, thecontroller 71 is capable of detecting the start of the operation of eachsub-disk drive 51β in the main housing 20 and the extension housing 30.When the start of the operation of each sub-disk drive 51β is detected,the controller 71 sends a command to each sub-disk drive 51β in the mainhousing 20 and the extension housing 30 through the FC-AL loop 60,requesting the sub-disk drive 51β to make a transition to the ‘Ready’operating state. Receiving the command, the sub-disk drive 51β startsoperating in the ‘Ready’ operating state, and thus gets connected to theFC-AL loop 60 at step S817.

As described above, all of the disk drives 51α and 51β in the mainhousing 20 and the extension housing 30 start to operate in the ‘Ready’state in which data can be read out from and written onto a disk 73.Then, when the controller 71 detects the start of the operation of eachof the disk drives 51α and 51β in the main housing 20 and the extensionhousing 30 by, for example, sending an inquiry through the FC-AL loop 60to each of the disk drives 51α and 51β, at step S818, the controller 71starts service for the host computer 40 by carrying out preparatoryprocesses such as starting required software.

===Other Embodiments===

It is not necessary to carry out the various functions of the controller71 and the sub-controller 81 in the ways described above. The variousfunctions can be implemented on either the controller 71 or thesub-controller 81; further, it is also possible to change theconfiguration for implementing the functions freely according to variouscircumstances.

The cooling device mounted in the basic housing 20 or the extensionhousing 30 does not have to be the cooling fan unit 58 described above.Instead, the cooling device can also be a cooling means of another type.For example, the cooling device can be a water-cooled cooling device ora cooling device employing a Peltier device.

The present invention can be applied not only to disk array devices, butalso to storage apparatuses using, for example, semiconductor disks,instead of the disk drives, as storage devices.

1.-15. (canceled)
 16. A method of controlling a storage apparatus, the storage apparatus including at least one housing A in which a storage device and a controller are provided, the storage device in the housing B including a plurality of storage units; at least one housing B in which another storage device and a cooling device are provided, the storage device in the housing B including a plurality of storage units; and a transmission path connecting the storage device and the controller of the housing A and the storage device of the housing B to enable communication therebetween; the method comprising: if one or more storage units of the storage device in the housing B are in a “power supply off” state wherein power supply to the one or more storage units of the storage device in the housing B is turned off, sending a command from the controller in the housing A to the housing B via the transmission path to lower an output of the cooling device in the housing B; and in response to the command from the controller in the housing A to lower the output, lowering the output of the cooling device in the housing B.
 17. A method of controlling a storage apparatus according to claim 16, wherein each storage unit of the storage device in the housing B comprises one or more disks mounted on a disk drive, and wherein rotation of the one or more disks is stopped in the “power supply off” state.
 18. A method of controlling a storage apparatus according to claim 16, wherein an average power consumption of the storage unit of the storage device in the housing B is zero in the “power supply off” state.
 19. A method of controlling a storage apparatus according to claim 16, wherein the cooling device in the housing B comprises a fan, and wherein lowering the output of the cooling device in the housing B comprises lowering a speed of the fan.
 20. A method of controlling a storage apparatus according to claim 16, further comprising monitoring, by the controller, an operating state of each storage unit of the storage device in the housing B to detect whether the storage unit is in the “power supply off” state.
 21. A method of controlling a storage apparatus according to claim 16, wherein the command to lower the output contains information of how many storage units of the storage device in the housing B are in the “power supply off” state, and wherein the output of the cooling device in the housing B is adjustably lowered based on the information contained in the command to lower the output.
 22. A method of controlling a storage apparatus according to claim 16, further comprising sending a command from the controller in the housing A via the transmission path to at least one storage unit in the housing B to change, from a “ready” operating state in which the storage unit can receive a command to read out or write data from or onto the storage unit, to a “not ready” operating state in which the storage unit cannot receive a command to read out or write data from or onto the storage unit.
 23. A method of controlling a storage apparatus according to claim 22, wherein each storage unit of the storage device in the housing B comprises one or more disks mounted on a disk drive, and wherein rotational speed of the one or more disks is reduced in the “not ready” operating state.
 24. A method of controlling a storage apparatus according to claim 22, wherein the at least one storage unit in the housing B changes from the “ready” operating state to the “not ready” operating state in response to the command from the controller in the housing A to change to the “not ready” operating state; and wherein at least one of the storage units of the storage device in the housing B is in the “not ready” operating state and remaining storage units of the storage device in the housing B are in the “power supply off” state.
 25. A method of controlling a storage apparatus according to claim 24, further comprising turning off power supply of a cooling device in the housing A.
 26. A method of controlling a storage apparatus according to claim 25, wherein at least one of the storage units of the storage device in the housing A is in the “power supply off” state and remaining storage units of the storage device in the housing A are not in the “power supply off” state; and further comprising transitioning the remaining storage units of the storage device in the housing A which are not in the “power supply off” state to the “power supply off” state by turning off power supply thereto.
 27. A method of controlling a storage apparatus according to claim 16, further comprising, in response to an instruction to turn off a main switch of the storage apparatus, the controller starting a destaging process of unwritten data left in a cache memory of the storage apparatus.
 28. A method of controlling a storage apparatus according to claim 27, further comprising, after the destaging process is completed, the controller in the housing A sending a command via the transmission path to at least one storage unit of the storage device in the housing A and at least one storage unit of the storage device in the housing B to transition to the “power supply off” state wherein power supply to the storage units in the “power supply off” state is turned off.
 29. A method of controlling a storage apparatus according to claim 28, further comprising turning off the power supply to the storage units in the “power supply off” state in response to the command to transition to the “power supply off” state.
 30. A method of controlling a storage apparatus, the storage apparatus including at least one housing A in which a storage device and a controller are provided, the storage device in the housing B including a plurality of storage units; at least one housing B in which another storage device and a cooling device are provided, the storage device in the housing B including a plurality of storage units; and a transmission path connecting the storage device and the controller of the housing A and the storage device of the housing B to enable communication therebetween; the method comprising: in response to an instruction to turn off a main switch of the storage apparatus, the controller in the housing A sending a command via the transmission path to at least one storage unit of the storage device in the housing A and at least one storage unit of the storage device in the housing B to transition to the “power supply off” state wherein power supply to the storage units in the “power supply off” state is turned off; turning off the power supply to the storage units in the “power supply off” state in response to the command to transition to the “power supply off” state; sending a command from the controller in the housing A to the housing B via the transmission path to lower an output of the cooling device in the housing B; and in response to the command from the controller in the housing A to lower the output, lowering the output of the cooling device in the housing B.
 31. A method of controlling a storage apparatus according to claim 30, further comprising, prior to sending the command to at least one storage unit of the storage device in the housing A and at least one storage unit of the storage device in the housing B to transition to the “power supply off” state, performing a destaging process of unwritten data left in a cache memory of the storage apparatus.
 32. A method of controlling a storage apparatus according to claim 30, wherein the command to lower the output contains information of how many storage units of the storage device in the housing B are in the “power supply off” state, and wherein the output of the cooling device in the housing B is lowered based on the information contained in the command to lower the output.
 33. A method of controlling a storage apparatus according to claim 30, further comprising sending a command from the controller in the housing A via the transmission path to at least one storage unit in the housing B to change, from a “ready” operating state in which the storage unit can receive a command to read out or write data from or onto the storage unit, to a “not ready” operating state in which the storage unit cannot receive a command to read out or write data from or onto the storage unit.
 34. A method of controlling a storage apparatus according to claim 33, wherein the at least one storage unit in the housing B changes from the “ready” operating state to the “not ready” operating state in response to the command from the controller in the housing A to change to the “not ready” operating state; wherein at least one of the storage units of the storage device in the housing B is in the “not ready” operating state and remaining storage units of the storage device in the housing B are in the “power supply off” state; and further comprising turning off power supply of a cooling device in the housing A.
 35. A method of controlling a storage apparatus according to claim 34, wherein at least one of the storage units of the storage device in the housing A is in the “power supply off” state and remaining storage units of the storage device in the housing A are not in the “power supply off” state; and further comprising transitioning the remaining storage units of the storage device in the housing A which are not in the “power supply off” state to the “power supply off” state by turning off power supply thereto. 